Error detecting device for printing telegraph receivers



April 11, 1939. J. A. SPENCER 2,153,737

ERROR DETECTING DEVICE FOR PRINTING TELEGRAPH RECEIVERS Filed June 10, 1957 INVENTOR JAMES A. SPENCER A'ITORNEY Watented Apr, ll, l3

TAT E S KTEE ERROR DETECTING DEVICE FOR PRINTING TELEGRAPH RECEIVERS James A. Spencer, Teaneck, N. J., assignor to Radio Corporation of America, a corporation oi Delaware Application June 10, 1937, Serial No. 147,3i28

7 Claims.

This invention relates to error detecting devices and has particularly to do with the provision of means for detecting errors of transirnission of code signals for printing telegraph apparatus. Printing telegraph code signals are especially susceptible to distortion and to mutilation when transmited by radio channels. It is, therefore, an object of my invention to provide means for detecting instances of mutilation of.

in code signals and to provide means either for preventing the receiving teletypewriter from printing characters erroneously or by enabling such a printef to indicate the reception of a mutilated signal by means of a special error indicating type impression on the record to be transcribed.

In carrying out my invention I prefer to make use of a signalling code having equal intervals for each character and having preferably seven or eight time intervals allotted to each code sigml so that a fixed number of marking time intervals may be maintained independently ,of the character designation for each code signal. A code signalling system in which the signals are of equal length and possess a fixed ratio other than 1 to 1 between the number of marking and spacing units. thereof has been disclosed in a copending application, Serial No. 78,348, filed May '7, 1936, by John B. Moore, et a1., and assigned to the assignee of the instant application.

0 A telegraph printer adapted tobe actuated by code signals of uniform length and having as many as seven or eight time elements in each code signal would require, of course, an equal number of selector bars. As explained in the application of Moore, et 2.1. above referred to, it is desirable that a fixed number of selector bars be actuated in making the selection of any character to be printed. If a shift key is employed, then seven units in the code signal would be sufiicient.

4.0 If no shift key is employed, then eight units would be required for difierently characterizing each code signal for ordinary communications purposes. My invention has particularly to do with a novel means for counting the number of marking impulses in each code signal sothat ii the fixed number or" such impulses is three, then the reception of any code signal having more or less than three marking impulses would be ef= fective upon the error detecting device of my in- (ii) vention so as to enable the receiving printer to print an error indicating character in place of the intended character.

I have found that an electrical circuit arrangement for carrying out the objects of my inven- 5 tion is preferable to a purely mechanical structure which might be designed for obtaining similar results. If the marking impulses are mechanically counted, it is true that it is possible to detect the errors which may occur in transmission, but an objection to the use of mechanical 5 means lies in theproblems of maintenance of such a. system as well as problems of maintaining a suitable printing speed. My invention is free from these objections because it operates on the basis of current differentials resulting from the 10 completion of a definite number of circuits, each completion being upon reception of a marking impulse. The error detector, therefore, operates under the direct control of the received signal.

My invention will now be described in more 15 detail, reference being made to the accompanying drawing, the sole figure of which shows a circuit ceiving printer may be employed which does not require a separate selector bar actuating magnet 90 for eachselector bar. In such case magnets 8 to M inclusive may be understood as constituting a bank of storage relays.

Each of the magnets 8 to Hi inclusive has as sociated therewith a pair of locking contacts l9 5 and an additional pair of make contacts 2b. One

contact of the latter pair is connected to a direct current source. The other contact of this pair leads to one or another of the several resistors R1 to R7 inclusive-and thence over a common i0 conductor through the winding of a relay 2!. This relay is adjusted to pull up its armature when any three of the relays B to it inclusive have been actuated thereby to feed current through at least three of the resistors Rl-R'i. t5

Another relay 22 is in circuit with the relay it but is adjusted to operate upon a strength resulting from the completion of more circuits in the resistance network Rl-R'l than there are normal marking elements in a code signal.

Still another relay 23 is in series with the relays 2i and 22 and is adjusted to operate on a current value derived from the completion of one or more circuits in the resistance network Rl-R'l.

The series circuit through the relays 2!, 22 and B5 23 leads eventually back to the direct current source and, say, the negative side thereof which, for the sake of simplicity in the description to follow, will be assumed to be grounded. The armature 24 of relay 23 is also grounded and when drawn up to its front contact 25 puts ground potential on one side of an operating magnet 26. The other side of the winding of magnet 26 leads to the armature of relay 22. The back contact of relay 22 is connected to the armature of relay 2|. The back contact of relay 2| and the front contact of relay 22 are both fed with positive potential through a resistor 21. designed that the operating magnet 26 may be energized upon the reception of a mutilated signal having either more or less than the standard number of marking impulses. When the magnet 26 is energized its armature is pulled up and clears a path for type lever 29 to drop into a slot in the code bar assembly 30. From this point the printing function is identical with a normally selected character. The type face associated with the special lever 29, however, is of special design indicating an error.

26 The mode of operation of the system in case of reception of a mutilated signal having more than the proper number of marking impulses is as follows:

Each of the relays 2|, 22 and 23 is actuated.

Positivc potential from the direct current source two of the resistors Ri-R1 to enable relays 2| and 22 to respond. However, current is fed from the positive side of the potential source through resistor 21, the back contact and armature of relay 2|, the back contact and armature of relay 22, and thence to the winding of magnet 26 on r the other side of which is the connection to the front contact 25 of the now energized relay 23 whose armature 24 completes this circuit to ground.

When the correct number of marking impulses has been received for the printing of a character of the message, relays 2| and 23 will be actuated but relay 22 will remain unenergized. In this case there will be no complete circuit from the positive side of the local source through the magnet 26 because the armature of. relay 2| is not against its back contact and the armature of relay 22 is not against its front contact. Hence no error indication will be made if the number of marking impulses in the received code signal is normal.

The locking circuits associated with the relays 8 to i l inclusive are opened at the end of each printing cycle by means of a contact 3| operated :y the printing bale oi the printer. This printing bale is not shown because it is well known in printing apparatus of conventional types.

It will be well understood by those skilled in the ,art that I may, if desired, operate contacts similar-to those shown in association with the relays 8-|4 merely by applying such contacts to the printer code bars. In this manner it will be possible to eliminate the relays 8-H and their associated locking circuits.

Since it can be seen that the relay 23 is always actuated upon the recelptoi one or more marking The system is sothey are to be understood as comprehended within the scope of the claims.

I claim:

1. In a printing telegraph receiving system, a printer, selective means for causing said printer to print a character in response to the reception of a single unmutilated multi-element code signal, a plurality of code-element responsi e devices, code element impulse counting means comprising a plurality of parallel impedance circuits each respectively closable by one of said responsive devices, and means including a plurality of error-detecting relays operable under control of currents through said impedance circuits, said currents being established upon reception of a single mutilated code signal for causing an errorindicating character to be printed in place of the character intended to be selected by the first said means.

2. In a printing telegraph receiving system, a printer having character selecting means responsive to a fixed number of marking elements of a uniform-length code signal, means for detecting instances of mutilation of the received signals, said means comprising a relay operable upon receipt of one or more marking impulses in a single one of said code signals, a second relay operable upon receipt of at least the normal number of markingimpulses in said code signal, and a third relay operable only upon receipt of a superfluous marking impulse in said cod signal, and means to print an error-indicating character in response to the cooperation of said relays when operated upon receipt of an abnormal number of marking impulses.

3. A printing telegraph apparatus having a plurality of de-coding members each actuable in response to the reception of a marking element or a code signal. type selecting elements each selectable upon the actuation of a fixed and uniformly normal number of said de-coding members, and means for indicating instances of mutilation of a code signal, said means comprising an electro-magnetic type-selecting element, a plurality of relays differentially biased, thereby to respond to currents of respectively difierentamplitudes, said relays being cooperatively actuable to energize the last said type-selecting element upon reception of an abnormal number of marking impulses in the time interval allotted to a single code signal, and a plurality of impedance circuits each closable respectively upon the actuation of one of said de-coding members, said circuits being connected in parallel with one another and in series with all of said relays thereby to control the number of said relays to be actuated in dependence upon the amplitude of the current traversing said relays, which amplitude is a function of the number of marking elements of the received signal.

4. In a telegraph system, code signal receiving apparatus, a receiving printer having characterselecting elements, means-including a plurality of de-coding members operable in response to unrepeated signals for controlling the actuation encore? nectec, c, reloy system in series with soicl imehcc circuits, one means operchie under con- W oi cruel releiy system when n mutilated cheructerjsignel is received for causing an error innicotine character to be prin 5. An arrangement in accordance with claim 4 end hsving three relays in said relay system, one of sold relays being operable by the minimum cur rent fed through one of sciclimpedances, a secand relcy being operable whenever current is fed thereto cimuitroneously through st least the numher oi solo impedcnces corresponding with the normal number of marking impulses in c. code signel, end a. third relay operable whenever current is fed; thereto simultaneously through a. nnmher of said impedsnces in excess of the normal number of said marking impulses.

c. in e telegraph prlnter'for equal length codes, means responsive to the reception of s mutilated signci hoving more or less than c. predetermined unvevrying number of marking impulses by which oil the code signals are characterined for making en error indication, said means comprising e piwclity of series-connec relays each operable when tee with current of u'predetermined litucie cine comprimng her on error l ing tyne memheroperohle when one only of ssicl reloys is, or oil oi" the score ore cctueteri, and means including o csreliel rearrangement of. incpedonces in series with said reieys cndi. closcole in accordance with the reception of men-king impulses in each signal for deter the number of sold relays to he octucted.

7. The method or eutomsticsliy indicating rt discrepetncy between the transmission and reception of equsl-length code signals, all of said signals as trnnsmittecl heme? characterized by on invariable number of marking elements erently disposecl with respect to the spacing elements, which comprises producing a first response at the receiving stotion upon reception of the first marking impulse in each corie signal, producing a. second response which nullities the eflect of the first response whenever the number of received marking impulses in n signel is normal, and producing a third response which restores the efifect of the first response whenever the number of received marking impulses in a. signal is excessive, and causing an error hnlicction to result from the efiects of either the first response or the third response.

it. Emit 

